<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Undefined 类型</title>
</head>
<body>
  <script>
    /* let message;

    console.log(message);
    console.log(age); */

    let message;

    console.log(typeof message);
    console.log(typeof age);
  </script>
</body>
</html>